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Chrysler Repair/'94 Concorde 3.3L - Hard miss with A/C on


QUESTION: Hi Roland!

I have a 1994 Chrysler Concorde 3.3L (non-flex) that has been exhibiting an intermittent problem.  I really don't know how to describe it except to say that it feels like the ignition was turned off and turned right back on, similar like a misfire but FAR more pronounced.  In fact, it sometimes almost feels like the car has been hit, it jerks/slams so hard!  

It always happens while I'm driving in a forward gear, and I am now realizing it only does so while the A/C is on.  Specifically, it lopes/jerks/slams precisely at the point when the A/C clutch cycles off.  Of course, since it is intermittent, I can observe 20 cycles and it won't do it but once or twice in that time.  But turn the A/C off, and it will drive smooth as butter.  Annoying.

Interestingly enough, it will do kind of the opposite when idling in park or neutral.  Occasionally, precisely when the clutch cycles off, the engine RPMs will jump up (maybe to 1200 or so) and immediately smooth back down to 700 or so.  Again, turn the A/C off and the idle is consistently smooth.

There is no check engine light on, and the ignition key dance only gives me a code 55.  I've also checked the ATC codes by setting the temp to 75 and holding down the correct three buttons until it flashes.  It was cool to hear it run its diagnostics.  But nope, nothing there either.  I've replaced both the camshaft and crankshaft sensors.  No change.  I've removed and cleaned the IAC valve, as well as the passage in the throttle body that it screws into.  Still no change.  I hooked up the A/C manifold gauges and monitored pressures.  Everything looks good, and A/C temps are awesome.  The engine RPMs are properly maintained when the A/C engages and usually when the clutch disengages.  It's just that one time when it drops out or flares up that is a doozie!

I am leaning toward replacing the input and output sensors on the transmission, but I hate to waste money on yet another needless repair.  Needless-to-say, I'm pretty baffled.  Any ideas?  :)

After reviewing the manual and your history of the problem, I am thinking that you may have some sort of a flaky ignition switch or that if indeed this doesn't happen except when you are running the air conditioner and it deactivates the compressor clutch which then causes the engine to falter, then I would wonder if there is a loose connection/short circuit intermittent which is triggered by the motion of the engine in response to the reduction in torque that was being demanded by the compressor.
The only electical aspect of the a/c system is to activate or deactivate the clutch, and that is solely dependent upon the AC being requested and by the AC pressure sensor showing that the pressure in the system is adequate. There is no electrical impact of the AC on the engine control function (e.g. the idle speed is not adjusted due to the air conditioner per se)  other than it will adjust itself to the lower idle speed that the compressor causes and likewise it will reduce the idle speed when the demand is lifted. It is possible that you have a dirty throttle body throat/butterfly plate or possibly a sticky automatic idle speed motor in the throttle body which is not responding as it should to bring about the proper idle when the load of the compressor is removed. So take a look at cleaning the throttle body throat and plate, and also remove the automatic idle speed motor and clean its tip and the passageway that it control to the side of the throttle body throat.
That is my suggestion at this point.

---------- FOLLOW-UP ----------

QUESTION: Thanks for such a quick response, Roland!  You've always been such a great help!

I had not thought of the ignition switch, so that's a great point to investigate.  I've already thoroughly cleaned the IAC/idle speed motor, as well as its passage into the throttle body.  Idle was generally more controlled/smooth after, but the intermittent problem persisted.

Interestingly, a new clue has just occurred.  I'm just not sure of how this fits into the equation -- then again, maybe the car's just falling apart in front of my eyes, LOL.  Ok, so I was just sitting in stopped traffic, engine running and transmission in Drive.  The A/C was on, and I just happened to be looking directly at the speedometer when the needle all of a sudden swung up to almost 35mph and immediately fell back down to the zero stop.  It did this so fast, that the needle actually bounced a few times off the zero stop, making a tap-tap-tap noise as it did so!

I looked around online and everyone's saying "transmission output speed sensor".  But how does that have anything to do with engine idle?  Am I looking at two different problems?  Or can they be related?  I keep thinking maybe as I'm driving at 70 on the interstate, if the speed sensor intermittently does that, that might be why the engine bucks so hard.  And similarly for when it is sitting still -- if the sensor does that, the car maybe thinks it is driving and tries to adjust idle upward some?

I am just grasping at straws here.  I plan to try every one of your suggestions, but thought I'd give that little update since it may help.

One would think that the transmission speed sensor would not cause the speedometer to jump like that when you aren't moving. It basically either pulses voltage, or not, when rotating or not and sitting still would be a 'not'. The possible cause would appear to me to be the CCD digital data bus which involves the engine and transmission intercommunication, perhaps having an intermittent open or short to ground or a voltage other than + or - 2.5v which is the bias on one or the other of its wires. The wiring is vast, unfortunately: bcm, pcm, tcm, cluster, air bag control, overhead console, anti-lock brake, ATC (the last three would be 'if equipped') are tied together by a pair of twisted wires. About the only simple thing would be if fuse #14 or 17 were flakey, so see if either might have a crack in its internal wire. Otherwise, a fault code readout with an OBD-I reader may be the next step.
On the ignition switch, try looking at the voltage on fuse #14 while you wiggle the key to see if it is stable.

---------- FOLLOW-UP ----------

QUESTION: Hi Roland,

Again I apologize for the delay in following-up with your answers. A lot occurred since 2011 that simply pushed it all on the back burner. I apologize again!

I will have the Concorde again tomorrow to repair some other issues, so I can pick up where we left off at. I'll follow-up with what I find.

Thanks again. You are the best!

Hi Tre,
It will be of interest to see what happened to the earlier situation. Although the AC would not be so comfortable this time of year, the AC does come into use when you ask for windshield defrost mode so that would be one way of testing the impact of the compressor without having to also have the cabin cooled all over.
I will not be around the computer tomorrow so try in the evening or Monday morning if something of interest comes up.

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Roland Finston


Get a Free Fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

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Yahoo Autos Group called The Chrysler Lebaron Club (co-moderator)

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